Filtration materials using fiber blends that contain strategically shaped fibers and/or charge control agents

ABSTRACT

A filtration material comprising a blend of polypropylene and acrylic fibers of round, flat, dog bone, oval or kidney bean shape in any size from 0.08 to 3.3 Dtex. A preferred blend contains about 50 weight percent polypropylene fibers and about 50 weight percent acrylic fibers. The fibers can be blended ranging from 90:10 to 10:90 polypropylene to acrylic. The shape contains 25 weight percent round, flat, oval, dog bone and kidney bean shapes. The fiber blend contains 25 weight percent of at least one size between 0.08 and 3.3 Dtex. Electret fibers incorporated within these blends have 0.02 to 33 weight percent of a charge control agent. These fibers can be used in producing electret material by corona or triboelectric charging methods.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/406,301 filed Oct. 25, 2010. This prior application is herebyincorporated by reference.

STATEMENT REGARDING FEDERALLY-SPONSORED RESEARCH AND DEVELOPMENT

(Not Applicable)

REFERENCE TO AN APPENDIX

(Not Applicable)

BACKGROUND OF THE INVENTION

The invention relates to electrostatic filtration media for gasfiltration, and more particularly to various combinations of syntheticfiber media of different cross-sectional shapes with and without chargecontrol agents, and methods of making fibers.

It is known in the filtration art that various kinds of fibers can beformed into a web or other nonwoven structure having tortuous pathsbetween the fibers through which a gas stream, such as air, is passed toremove particulate matter from the gas stream. The particulate matter inthe gas flowing through the paths in the web is retained on the upstreamside of the web, or within the tortuous paths of the web due to the sizeof the particles relative to the paths' diameters.

Synthetic fibers come in various cross-sectional shapes including, butnot limited to, round, flat, trilobal, kidney bean, dog-bone, bowtie,ribbon, 4DG (multiple grooves along a fiber's length), hollow, sheathcore, side by side, pie wedge, eccentric sheath core, islands and threeisland. It is known to charge various blends of fibers electrostaticallyto further retain particulate matter through electrostatic attractionbetween the fibers and the particles. Such blends and other filtrationimprovements are shown in U.S. Pat. No. 6,328,788 to Auger, U.S. Pat.No. 4,798,850 to Brown, U.S. Pat. No. 5,470,485 to Morweiser, et al.,and U.S. Pat. No. 5,792,242 to Haskett, all of which are incorporatedherein by reference.

Electrostatic (“electret”) filter media have increased efficiencywithout necessarily increasing the amount of force it takes to push theair though the filtration media. The “pressure drop” of media is thedecrease in pressure from the upstream side of the media to thedownstream side. The more difficult it is to force air through themedia, the greater the pressure drop, and the greater use of energy toforce air through the media. Therefore, it is generally advantageous todecrease pressure drop.

Electrostatically charged media is used in many different applicationsand in many different filters. The electrostatic charge is appliedeither by oxidatively treating the fibers, such as by passing the fibersthrough a corona, or by triboelectric charging, which is a type ofcontact electrification in which certain materials become electricallycharged after they come into contact with a dissimilar material (such asthrough rubbing) and are then separated. The polarity and strength ofthe produced charges differ according to the materials, surfaceroughness, temperature, strain, and other properties. Such electrostaticcharges tend to dissipate over time, and this leads to reducedefficiency in removing particles from the air stream. In particular, theefficiency of removing small particles (below 10 microns) is reduced ascharges dissipate.

Currently, passive electrostatic filter media works mainly on theprinciple of friction from air passing over fibers and inherent staticelectricity in the polymer itself. Static electrification is not causedmerely by air flow impacting a solid surface. In many cases apolypropylene honey-combed netting, typically with woven monofilamentapproximately 0.01 inches in diameter, is used in different layers or inconjunction with a urethane foam or a high loft polyester which also hasinherent static charges. In the more efficiently static charged fiberfilters, each fiber has both positive and negative charges. Such fibersare 1 to 30 denier in size, or approximately 0.00049 to 0.00268 inchesin diameter. Generally these types of filters are more expensive than adisposable type, lasting about three months in a residential heating,ventilation and air conditioning (HVAC) unit. The efficiencies of suchelectret filters are known to be very good, with approximately 34% to40% dust spot efficiency.

Charge control agents have been used to control static charges inimaging applications, such as photostatic and Xerographic(electrophotographic) processes. Positive and negative charge-controlagents, charge directors, charge additives, charge adjuvants,zwitterionic materials, polar additives, dielectric substance andelectroconductivity-providing agents, (ECPA's), all are referred to ascharge control agents (CCA's) and are known for use in the followingapplications with some CCA's on some materials: powder toner, powdercoating or powder electrophotographic toner, liquid toner, liquiddeveloper, chargeable toner, electrophotographic recording, powderpaint, developing toner, electrostatic copying, electret fiber material,electrophoretic image display, impulse ink jet printing, sprayablepowder coating and electrostatic image developer.

The prior art filtration materials provide sufficient filtration formany environments. However, where the electrostatic charge must beretained for long periods or where the penetration through thefiltration material must be below a particular percentage, the prior artdoes not suffice, or is prohibitively expensive to manufacture.Therefore, the need exists for a filtration material that provides theneeded performance at a feasible cost to manufacture.

BRIEF SUMMARY OF THE INVENTION

Improvements in the efficiency of gas filtration media are achieved byforming filtration media fibers in cross-sectional shapes that areunique and advantageous. Additionally, unique and advantageouscombinations of fibers with particular cross-sectional shapes and chargecontrol agents are disclosed. Furthermore, disclosed herein are newmethods of making fibers and fibers with charge control agents. Stillfurther, charge control agents not previously known for use infiltration media are disclosed.

This invention improves the overall efficiency of the filtration mediaby enhanced charging modifications and by combining different sizes andshapes of fibers. It is part of the invention to optimize the size andshape of fibers to optimize performance, as measured by efficiency. Theinvention provides several different advancements of media manufacturingand chargeability of these media, increases in efficiencies based onelectrostatic technology, and several different methods of enhancing themedia charge and efficiency. The novel modified materials produced bydoping polymers and the introduction of these polymers to anelectrostatic field result in increased air filtration efficiencies.

Applicant herein incorporates the following United States Patents byreference: U.S. Pat. Nos. 5,563,016; 5,069,994; 5,021,473; 5,147,748;5,502,118; 5,501,934; 5,693,445; 5,783,346; 5,482,741; 5,518,852;5,800,602; 5,585,216; 4,404,270; 4,206,064; 5,318,883; 5,612,161;5,681,680; 5,061,585; 4,840,864; 5,192,637; 4,833,060; 4,394,430;5,935,754; 5,952,145; 5,750,306; 5,714,296; 5,525,450; 5,525,448;4,707,429; 5,045,425; 5,069,995; 4,760,009; 5,034,299; 5,028,508;5,573,882; 5,030,535; 5,026,621; 5,364,729; 5,407,775; 5,549,007;5,484,679; 5,409,796; 5,411,834; 5,308,731; 5,476,743; 5,445,911;5,035,972; 5,306,591; 5,407,774; 5,346,796; 5,393,635; 4,496,643;4,977,056; 5,051,330; 5,266,435; 5,411,576; 5,645,627; 5,558,809;5,935,303; 6,102,457; 6,162,535; 6,444,312; 6,780,226; 6,802,315;6,808,551; 6,858,551; 6,893,990; 6,926,961; 7,498,699; 7,666,931 andApplicant also incorporates herein by reference European ApplicationPublication Number EP-A-0 347 695.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a magnified photograph of an end of a dry spun, halogen freeacrylic fiber having a dog-bone-shaped cross section. A “dog-bone” crosssection is defined herein as an elongated shape having opposite endsthat are wider than a central region between the two ends, and thecentral region has a necked-down shape with both sides curving inwardly.

FIG. 2 is a magnified photograph of a plurality of fibers having akidney-bean-shaped cross section. A “kidney-bean” cross section isdefined herein as an elongated shape having opposite ends that are wideror about as wide as a central region between the two ends, and thecentral region has a necked-down shape with only one side curvinginwardly substantially.

FIG. 3 is a magnified photograph of a plurality of ends of wet spunacrylic fibers having dog-bone-shaped cross sections.

FIG. 4 is a photograph showing a plurality of clusters of fibers havinga three dimensional crimp.

FIG. 5 is a photograph showing a plurality of clusters of fibers havinga two dimensional crimp.

FIG. 6 is a graph illustrating the rate at which resistance to the flowof gas through two filtration media changes with increases in thevelocity of gas at the face of the media.

In describing the preferred embodiment of the invention which isillustrated in the drawings, specific terminology will be resorted tofor the sake of clarity. However, it is not intended that the inventionbe limited to the specific term so selected and it is to be understoodthat each specific term includes all technical equivalents which operatein a similar manner to accomplish a similar purpose. For example, theword connected or terms similar thereto are often used. They are notlimited to direct connection, but include connection through otherelements where such connection is recognized as being equivalent bythose skilled in the art.

DETAILED DESCRIPTION OF THE INVENTION

U.S. Provisional Patent Application Ser. No. 61/406,301 is incorporatedherein by reference.

Permanent charges on fibers are provided in air filter media bycompounding or doping charge control agents (CCA's) into the fiber orcoating surfaces of fibers or materials utilized in the media withCCA's. CCA's are added to the fibers according to the invention in aconventional manner, except as described otherwise below. For example,the addition of CCA's to polypropylene fibers is accomplished by addingthe CCA's in particulate form (powders and/or granules) to a melt justbefore extruding the melt and mixing thoroughly. Therefore, the CCAparticles that are suspended and well-distributed in the melt are, tosome degree, found at the surface of the fibers after extrusion.

The invention provides a novel method to enhance the chargeability offibers. The object of this invention is to induce a charge field notonly on the surface of the fiber, but to provide an electrostatic chargebelow the surface of the fiber. The invention accomplishes thisobjective in one embodiment by adding about 0.1 to 50 percent (by weightof materials) CCA's to polymer fibers. For example, when melting a CCAthat has a melt temperature above the polymer's melting temperature, amicron-sized powder is introduced and in most cases 10-20% of the powdercomes to the surface, which leaves 80 to 90 percent of the powder belowthe surface. This method of enhancing the charges can be utilized inmost of the filtration media used today.

The CCA's operate by triboelectric or corona charging of particles, andthe effects of the CCA's are superior when CCA's are on the outside ofthe fibers. The preferred concentration of CCA particles as a percentageof the weight of the completed fibers is between about 0.02% and about50%, a more preferred concentration is between about 0.1% and about 40%and a most preferred concentration is between about 0.3% and about 10%.

Some of the polymer fibers used in filtration media that are suitablefor charging include polypropylene, polyesters, polyethylene andcross-linked polyethylene, polycarbonates, polyacrylates,polyacrylonitriles, polyfumaronitrile, polystyrenes, styrene maleicanhydride, polymethylpentene, cyclo-olefinic copolymer or fluorinatedpolymers, polytetrafluoroethylene, perfluorinated ethylene andhexfluoropropylene or a copolymer with PVDF like P(VDF-TrFE) orterpolymers like P(VDF-TrFE-CFE). Propylene, polyimides, polyetherketones, cellulose ester, nylon and polyamides. Polymethacrylic,poly(methylmethacrylate), polyoxymethylene, polysulfonates, acrylic,styrenated acrylics, pre-oxidized acrylic, fluorinated acrylic, vinylacetate, vinyl acrylic, ethylene vinyl acetate, styrene-butadiene,ethylene/vinyl chloride, vinyl acetate copolymer, latex, polyestercopolymer, carboxylated styrene acrylic or vinyl acetate, epoxy, acrylicmultipolymer, phenolic, polyurethane.

One or more different fibers blended in a filtration media can contain acharge control agent. This can be one fiber, two fibers, three fibers,four fibers, five fibers or six fibers in the media that are ofdifferent composition, some or all of which contain a CCA. These CCA'sinclude but are not limited to metal salt of aluminum or magnesium, leadzirconate titanate, potassium niobate, lithium niobate, lithiumtantalate, sodium tungstate, unsaturated carboxylic acid or derivativethereof, unsaturated epoxy monomer or silane monomer, maleic anhydride,monoazo metal compound, alkyl acrylate monomers, alkyl methacrylatemonomers, polytetrafluoroethylene, alkylene, arylene, aryleneialkylene,alkylenediarylene, oxydialkylene or oxydiarylene, polyacrylic andpolymethacrylic acid compound, organic titanate, quaternary phosphoniumtrihalozincate salts, organic silicone complex compound, dicarboxylicacid compound, cyclic polyether or non-cyclic polyether andcyclodextrin, complex salt compound of the amine derivative,ditertbutylsalicyclic acid, potassium tetaphenylborate, potassium bisborate, sulfonamides and metal salts, cycloalkyl, alumina particlestreated with silane coupling from group consisting of dimethyl siliconecompound, azo dye, phthalic ester, quaternary ammonium salt, carbazole,diammonium and triammonium, hydrophobic silica and iron oxide, phenyl,substituted phenyl, naphthyl, substituted naphthyl, thienyl, alkenyl andalkylammonium complex salt compound, sodium dioctylsulfosuccinate andsodium benzoate, zinc complex compound, mica, monoalkyl and dialkyl tinoxides and urthene compound, metal complex of salicyclic acid compound,oxazolidinones, piperazines or perfluorinated alkane, lecigran MT,nigrosine, fumed silca, carbon black, para-trifluoromethyl benzoic acidand ortho-fluoro benzoic acid, poly(styrene-co-vinylpyridinium toluenesulfonate), methyl or butyltriphenyl complex aromatic amines,triphenylamine dyes and azine dyes, alkyldimethylbenzylammonium salts.

A charge director is selected from the group consisting of lecithin,basic barium petronate and calcium petronate, sulfonate compounds,isopropylamine salt of dodecylbenzensulfonic acid or diethylammoniumchloride and isopropylamine dodecylbenzenesulfonate, quaternizedammonium AB diblock copolymer, polyacrylic acid, silicone carbide, PTFEparticles, aluminum oxide, cross linked polymethacrylicate resin, silicaacrylate complex, poly acrylic acid and amorphous silica. Yttrium (III)2-ethylhexanoate, a Yttrium (III) acetylacetonate hydrate, Yttrium (III)tris (2,2,6,6-tetramethy-3,5-heptanedionate) or a Scandium(III)tris(2,2,6,6-tetramethy-3,5-heptanedionate) hydrate, Scandium, Yttrium,Lutetium, and Lawrencium, metal compounds of aromatic carboxylic acidssuch as salicylic acid, alkylsalicylic acid, dialkylsalicylic acid,naphthoic acid, and dicarboxylic acids, the metal salts and metalcomplexes of azo dyes and azo pigments, polymer compounds that have asulfonic acid group or carboxylic acid group in side chain position,boron compounds, urea compounds, silicon compounds and calixarene.

The positive-type charge control agents can be exemplified by quaternaryammonium salts, polymer compounds having a quaternary ammonium salt inside chain position, guanidine compounds, nigrosin compounds, andimidazole compounds, metal complexes of organic compounds having acarboxyl group or a nitrogen-containing group, metallized dyes,nigrosine and charge control resins, quinone compounds (e.g.,p-benzoquinone, chloranil, bromanil, and anthraquinone),tetracyanoquinodimethane compounds, fluorenone compounds (e.g.,2,4,7-trinitroflurenone), xanthone compounds, benzophenone compounds,cyanovinyl compounds, and ethylenic compounds, electron hole transportcompounds such as triarylaamine compounds, benzidine compounds,arylalkane compounds, aryl-substituted ethylene compounds, stilbenecompounds, anthracene compounds, and hydrazone compounds, a carboxylgroup or a salt thereof, a phenyl group or a salt thereof, a thiophenylgroup or a salt thereof and a sulfonic group or a salt thereof,inorganic particles include silicon dioxide (silica), aluminum oxide(alumina), titanium oxide, zinc oxide, tin oxide, barium titanate andstrontium titanate yttrium and stearic acid, stearic acid and aluminum,poly (N-vinylcarbazole) and polysilane, aromatic hydroxycarboxylic acidand a calcium compound, fatty acid metal salt of aluminum or magnesium,fluorenone compounds, quinone compounds, alkylsalicylic acid derivative,a compound being a zincified alkylsalicylic acid derivative which is analkylphenol derivative having a carboxyl group.

Examples of waxes include, but are not limited to, those listed herein,and include polyolefins such as polyethylenes, and the like, such asthose commercially available from Allied Chemical and Baker PetroliteCorporation, and the Daniels Products Company, Epolene N-15.TM.commercially available from Eastman Chemical Products, Inc.

Examples of functionalized waxes include amines, amides, for exampleAqua Superslip 6550, Superslip 6530 available from Micro Powder Inc.,fluorinated waxes, for example Polyfluo 190, Polyfluo 200, Polyfluo523XF, Aqua Polyfluo 411, Aqua Polysilk 19, Polysilk 14 available fromMicro Powder Inc., mixed fluorinated, amide waxes, for exampleMicrospersion 19 also available from Micro Powder Inc., imides, esters,quaternary amines, carboxylic acids or acrylic polymer emulsion, forexample Joncryl 74, 89, 130, 537, and 538, all available from SC JohnsonWax, chlorinated polyethylenes available from Allied

Chemical, Petrolite Corporation and SC Johnson Wax. Such waxes canoptionally be fractionated or distilled to provide specific cuts thatmeet viscosity and/or temperature criteria wherein the upper limit ofviscosity is 10,000 cps and the upper limit of temperature is 100° C.

The natural ester waxes are exemplified by candelilla wax, as ozokerite,ceresin, rice wax, Japanese wax, jojoba oil, beeswax, lanolin, castorwax, montan wax, and derivatives of the preceding. Modified waxes inaddition to the preceding are exemplified by polyalkanoic acid amides(ethylenediamine dibehenylamide), polyalkylamides (tristearylamide oftri-mellitic acid), and dialkyl ketones, distearyl keto, aliphatichydrocarbon waxes such as low molecular weight polyethylenes, lowmolecular weight polypropylenes, low molecular weight olefin copolymers,microcrystalline waxes, paraffin waxes, and Fischer-Tropsch waxes,oxides of aliphatic hydrocarbon waxes, such as oxidized polyethylenewax, waxes having an aliphatic acid ester as the main component, such asaliphatic hydrocarbon-type ester waxes, waxes obtained by the partial orcomplete deacidification of an aliphatic acid ester, such as deacidifiedcarnauba wax, partial esters between aliphatic acids and polyhydricalcohols, such as monoglyceryl behenate, and hydroxyl- functional methylester compounds obtained by the hydrogenation of plant oils and fats.

The synthetic ester waxes are exemplified by monoester waxes synthesizedfrom straight-long-chain saturated aliphatic acids andstraight-long-chain saturated alcohols. The straight-long-chainsaturated aliphatic acid used is preferably represented by the generalformula C_(n)H_(2n)+1COOH where n is about 5 to 28. Thestraight-long-chain saturated alcohol used is preferably represented bythe general formula C_(n)H_(2n)+1OH where n is about 5 to 28. Thestraight-long-chain saturated aliphatic acid is specifically exemplifiedby caprylic acid, undecylic acid, lauric acid, tridecylic acid, myristicacid, palmitic acid, pentadecylic acid, heptadecanoic acid,tetradecanoic acid, stearic acid, nonadecanoic acid, arachic acid,behenic acid, lignoceric acid, cerotic acid, heptacosanoic acid,montanic acid, and melissic acid. Ester waxes having two or more esterbonds in each molecule are exemplified by trimethylolpropanetribehenate, pentaerythritol tetrabehenate, pentaerythritol diacetatedibehenate, glycerol tribehenate, 1,18-octadecanediol bisstearate, andpolyalkanol esters (tristearyl trimellitate, distearyl maleate).Modified waxes in addition to the preceding are exemplified bypolyalkanoic acid amides (ethylenediamine dibehenylamide),polyalkylamides (tristearylamide of tri-mellitic acid), and dialkylketones, distearyl keto, metal complex salts of monoazo dyes, metalcompounds of nitrofumic acid and salts thereof, salicylic acid,alkylsalicylic acids, dialkylsalicylic acids, naphthoic acid,dicarboxylic acids and so forth, boron compounds, urea compounds,silicon compounds, carixarene, sulfonated copper phthalocyaninepigments, chlorinated paraffin, low and high molecular weightfluorinated waxes.

There is also an advantage to a special crimp and crimping process indry and wet spun acrylic fibers. Within the manufacturing process ofstandard wet and dry spun acrylic fibers, the fibers are crimped (bentpermanently) with a so-called “tongue crimper”. The crimp forms bends inthe fibers that allow the fibers to lie substantially within a plane.This is referred to herein as “two dimensional” crimping, because fibersso crimped, if placed on an x-y-z axis, will extend substantially in thex and y dimensions, but not substantially in the z direction. Forexample, a two dimensionally crimped wet spun acrylic fiber extends manymillimeters in the x direction and many millimeters in the y direction.However, a two-dimensionally crimped fiber will only extend about onemillimeter or less in the z direction.

In a unique crimping process of the invention, a new kind of crimpingtakes place which has a substantial improvement on filtrationperformance. An injection tube with steam and high negative pressurepulls the fiber material at a high speed. At the end of this injectiontube the material gets the chance to relax suddenly by impact and thereduced pressure. This has the effect that the material compressesitself and forms a three-dimensionally crimped fiber. A threedimensionally crimped fiber is a fiber that, if placed on an x-y-z axis,extends similar orders of magnitude in all three directions. Thus, sucha fiber might extend 8 millimeters in the x direction, 15 millimeters inthe y direction and 4 millimeters in the z direction. Such a dry spunacrylic fiber product is currently made having three dimensionalcrimping, and is sold under the product name DRALON X101. However, toApplicant's knowledge such fibers are not conventionally used infiltration applications, but only carpet and textile applications.

The three-dimensionally crimped fibers used herein in a filtration medianot only takes less needling to form the media, but also advantageouslyform “open” media, thereby allowing more air flow through the media withless resistance, thereby supplying high efficiency filtration with lessresistance to the air flow. In summary, a filtration media made withsuch fibers achieves high efficiency with low pressure drop.

Another method involving wet spun acrylic fibers crimped twodimensionally includes the same tongue-crimping process of theconventional wet spun acrylic fiber process, but with a difference.Instead of adding conventional surfactants and/or lubricants to thewater of the wet spinning apparatus, the method includes the addition ofa special organic wax to the water at a desired percentage of about 0.5%to about 5.0% to permit the crimping action but not enough to render thefiber unusable due to too much finish on the fiber to charge. Thepercentage of the organic wax on the fiber surface is about 0.5% toabout 2% by weight of the finished fibers. The organic wax left on thefibers serves as a CCA and provides superior charge stability.

Testing below compares various fiber blends and their performancedifferences. All the testing is performed under the following parameters(except for test number 1):

-   -   All materials tested were produced to 70 grams per square meters    -   Fractional efficiency performed with particles sizes of; 0.3,        0.5, 5 and 10 micron.    -   Test velocity of 60 FPM    -   Voltage measurements performed with Chapman Corporation        Voltmeter

Test 1 is a comparison of blends of polypropylene and modacrylic fiberswith and without CCA's to determine the effects of the CCA's onefficiencies.

Formula A was standard 50/50 mixture of polypropylene and modacrylicwith 5 percent fumed silica extruded as a CCA into the polypropylenefiber. Fibers of 3 and 2.5 denier were carded together to produce a 300gram per square meter sample. The material was tribo-electricallycharged on a sample card generating approximately 1,100 volts and after30 days the charge state of 900 volts was measured. Both positive andnegative charges were maintained.

Formula B consisted of fibers identical to the media of Formula A exceptthat the polypropylene fibers in Formula B were undoped. Testing wasperformed on a TSI 8130 at 95 LPM.

Efficiency Percentages charged media Doped and Charged Media Undoped at0.1 micron

Formula A Doped Formula B Undoped Penetration .0375 .10 Efficiency99.9625% 99.90%

Test 1 shows that the use of charge control agent can help with theperformance of an electrostatic filter material by increasing thepenetration.

Tests 2 through 7 below use the same Formula A media, which allows oneto compare this media to many others, and allows the others to becompared to one another.

Test 2 is a comparison of fiber blends containing polypropylene andacrylic fibers, where the fibers of Formula A are without CCA's and thefibers of Formula B contain CCA's.

Formula A included 25% PP round fibers 2.8 Dtex; 25% PP round fibers 2.5Dtex; 25% acrylic wet spun kidney bean shaped fibers 2.2 Dtex; and 25%acrylic dry spun dog bone shaped fibers 3.3 Dtex.

Formula AB included 25% PP round fibers 2.8 Dtex; 25% PP round fibers2.5 Dtex; 25% acrylic wet spun kidney bean shaped fibers 2.2 Dtex with2% organic wax applied when crimping fibers; and 25% acrylic dry spundog bone shaped fibers 3.3 Dtex.

Efficiency of Particle Formula Efficiency of Size (micron) A (%) FormulaAB (%) .3 48.78 61.98 .5 62.88 73.68 5 84.38 89.24 10 99.12 99.64

The material was tribo-electrically charged to approximately 1,400volts. After 120 days the charge was measured to be a positive 1,245 tonegative −1,120 volts. Both negative and positive charges werethroughout the material. With charge control agent selection, positiveefficiencies were achieved demonstrating the improved effect by chargingthe fibers. Considerable improvements to efficiency are seen between 0.3micron and 10 micron. Test 2 shows that wet spun kidney bean shapedfibers with 2% organic wax outperform the wet spun kidney bean shapefibers without CCAs.

Test 3 is like Test 2, but where the CCA's were on the polypropylenefibers rather than the acrylic fibers.

Formula A included 25% PP round fibers 2.8 Dtex; 25% PP round fibers 2.5Dtex; 25% acrylic wet spun kidney bean shaped fibers 2.2 Dtex; and 25%acrylic dry spun dog bone shaped fibers 3.3 Dtex.

Formula AC included 25% PP round fibers 2.8 Dtex with 2% non-organicwax; 25% PP round fibers 2.5 Dtex; 25% acrylic wet spun kidney beanshaped fibers 2.2 Dtex; and 25% acrylic dry spun dog bone shaped fibers3.3 Dtex.

Efficiency of Particle Formula Efficiency of Size (micron) A (%) FormulaAC (%) .3 46.23 62.38 .5 61.14 74.52 5 81.69 90.72 10 99.06 99.73

The material was tribo-electrically charged to approximately 1,500volts. After 120 days the charge was measured at a positive 1,080 tonegative −1,385 volts. Both negative and positive charges werethroughout the material. With charge control agent selection, positiveefficiencies were achieved demonstrating the improved effect by chargingof the fibers. Considerable improvement to efficiency is seen between0.3 and 10 microns. Test 3 shows that adding the CCA's to the round PPfiber media results in better performance than when applying CCA's tothe acrylic fibers.

Test 4 is like Test 2, but where the CCA's are applied to dog boneshaped fibers rather than kidney bean shaped fibers in Test 2.

Formula A included 25% PP round fibers 2.8 Dtex; 25% PP round fibers 2.5Dtex; 25% acrylic wet spun kidney bean shaped fibers 2.2 Dtex; and 25%acrylic dry spun dog bone shaped fibers 3.3 Dtex.

Formula AD included 25% PP round fibers 2.8 Dtex; 25% PP round fibers2.5 Dtex; 25% acrylic wet spun dog-bone shaped fibers 3.3 Dtex with 2%organic wax applied when crimping fibers; and 25% acrylic dry spun dogbone shaped fibers 3.3 Dtex.

Efficiency of Particle Formula Efficiency of Size (micron) A (%) FormulaAD (%) .3 46.23 62.38 .5 61.14 76.52 5 81.69 90.67 10 99.06 99.9

The fibers were formed with the wax added to the outside of the fiberduring the crimping process. The material was tribo-electrically chargedto approximately 1,700 volts. After 30 days the charge was measured atpositive 1,200 to negative −1,645 volts. Both negative and positivecharges were throughout the material. With charge control agent plusfiber shape selection, positive efficiencies were achieved demonstratingthe improved effect by charging and shape of the fiber. Considerableimprovement to efficiency is seen between 0.3 and 10 microns. Test 4shows that wet spun dog bone shaped fiber media performs better than wetspun kidney bean shaped fiber media with the organic wax on the outsideof both fibers. This test also shows that when CCA's are added and theshape of the fiber is chosen carefully, performance is affected morethan when only the shape of the fibers is chosen.

Test 5 compares the effect of using shaped polypropylene fibers to usinground polypropylene fibers when both are in a blend with shaped acrylicfibers.

Formula A included 25% PP round fibers 2.8 Dtex; 25% PP round fibers 2.5Dtex; 25% acrylic wet spun kidney bean shaped fibers 2.2 Dtex; and 25%acrylic dry spun dog bone shaped fibers 3.3 Dtex.

Formula AE included 25% PP dog bone shaped fibers 2.8 Dtex with 2%non-organic; 25% PP round fibers 2.5 Dtex; 25% acrylic wet spun kidneybean shaped fibers 2.2 Dtex; and 25% acrylic dry spun dog bone shape 3.3Dtex.

Efficiency of Particle Formula Efficiency of Size (micron) A (%) FormulaAE (%) .3 46.16 47.16 .5 62.63 78.31 5 83.21 93.14 10 99.07 99.9

The standard PP fibers were extruded with 2% PVDF added. The materialwas tribo-electrically charged to approximately 1,800 volts. After 30days the charge was measured at a positive 1,400 to negative −1,700volts. Both negative and positive charges were throughout the material.

With 2% charge control agent plus selected fiber cross-sectional shape,positive efficiencies were achieved, thereby demonstrating the improvedeffect by charging and by selecting the shape of the fiber. Considerableimprovement in efficiency is seen between 0.3 and 10 microns.

With a charge control agent plus strategically selected fiber shape,positive efficiencies were achieved, thereby demonstrating the improvedeffect by charging and shape of the fiber. Considerable improvement toefficiency is seen between 0.3 and 10 microns. Test 5 shows that 2.8Dtex PP dog-bone fiber media performs better than 2.8 Dtex round fiberwhen both have non-organic wax added to the fiber.

Test 6 compares the effect of CCA's on blends when shaped acrylic fibersare combined with round PP fibers and the CCA's are applied to the PPfibers.

Formula A was 25% PP round fibers 2.8 Dtex; 25% PP round fibers 2.5Dtex; 25% acrylic wet spun kidney bean shape fibers 2.2 Dtex; and 25%acrylic dry spun dog bone shape 3.3 Dtex.

Formula AF was 25% PP round fibers 2.8 Dtex with 2% PVDF; 25% PP roundfibers 2.5 Dtex; 25% acrylic wet spun kidney bean shaped fibers 2.2Dtex; and 25% acrylic dry spun dog bone shaped fibers 3.3 Dtex.

Efficiency of Particle Formula Efficiency of Size (micron) A (%) FormulaAF (%) .3 40.21 72.89 .5 59.47 81.72 5 78.28 96.41 10 98.71 99.9

The material was tribo-electrically charged to approximately 1,800volts. After 30 days the charge was measured at a positive 1,300 tonegative −1,680 volts. Both negative and positive charges werethroughout the material.

With charge control agent selection, positive efficiencies wereachieved, thereby demonstrating the improved effect of charging thefibers. Considerable improvement in efficiency is seen between 0.3 and10 microns. Test 6 shows that 2.8 Dtex PP round fibers with 2% PVDFperform better than 2.8 Dtex round fiber without PVDF. This test alsoshows that PVDF performs better than wax-type CCA's when comparing Test6 results with Tests 2, 3, 4 and 5.

Test 7 measures the effect of adding CCA's to shaped PP fibers in ablend of round and shaped PP fibers with shaped acrylic fibers, ascompared to round PP fibers with shaped acrylic fibers and no CCA's.

Formula A included 25% PP round fibers 2.8 Dtex; 25% PP round fibers 2.5Dtex; 25% acrylic wet spun kidney bean shaped fibers 2.2 Dtex; and 25%acrylic dry spun dog bone shaped fibers 3.3 Dtex.

Formula AG included 25% PP dog bone shaped fibers 2.8 Dtex with 2% PVDF;25% PP round fibers 2.5 Dtex; 25% acrylic wet spun kidney bean shapedfibers 2.2 Dtex; and 25% acrylic dry spun dog bone shaped fibers 3.3Dtex.

Efficiency of Particle Formula Efficiency of Size (micron) A (%) FormulaAG (%) .3 42.41 73.71 .5 60.81 83.32 5 79.91 97.48 10 99.06 99.9

The fibers were spun with the wax added to the outside of the fiberduring the crimping process. The material was tribo-electrically chargedto approximately 1,900 volts.

After 30 days the charge was measured at a positive 1,365 to negative−1,720 volts, with both negative and positive charges throughout thematerial.

With charge control agent plus fiber shape selection, positiveefficiencies were achieved, thereby demonstrating the improved effect bycharging and shape of the fiber. Considerable improvement to efficiencyis seen between 0.3 and 10 microns.

Test 7 shows that 2.8 PP dog bone shaped fiber media with 2% PVDFperforms better than 2.8 PP round fibers without PVDF and better thanTest 6 in which only round PP fibers with PVDF were used. This test alsoshows that dog bone shaped fiber media with the CCA PVDF performs betterthan standard round fibers with or without PVDF.

Test 8 compares fiber blends with a small amount of round PP fibers withCCA's added combined with a larger amount of shaped PP fibers and shapedacrylic fibers to an identical blend without CCA's.

Formula B included 10% PP round fibers 1.4-1.7 Dtex; 40% PP round fibers2.5 Dtex; 25% acrylic wet spun kidney bean shaped fibers 2.2 Dtex; and25% acrylic dry spun dog bone shaped fibers 3.3 Dtex.

Formula BA included 10% PP round fibers 1.4-1.7 Dtex with 2% PVDF; 40%PP round fibers 2.5 Dtex; 25% acrylic wet spun kidney bean shaped fibers2.2 Dtex; and 25% acrylic dry spun dog bone shaped fibers 3.3 Dtex.

Efficiency of Particle Formula Efficiency of Size (micron) A (%) FormulaBA (%) .3 48.82 81.38 .5 66.29 91.68 5 82.18 98.16 10 98.91 99.9

The material was tribo-electrically charged to approximately 2,000volts. After 30 days the charge was measured at a positive 1,395 tonegative −1,770 volts, with both negative and positive chargesthroughout the material.

With charge control agent plus fiber shape and size selection, positiveefficiencies were achieved, thereby demonstrating the improved effect bycharging, shape and size of the fiber. Considerable improvement toefficiency is seen between 0.3 and 10 microns.

Test 8 shows that round micro denier fibers with PVDF perform betterthan small fibers without PVDF. A small amount of micro fibers help theperformance. This test shows that micro fibers help performance withoutCCA's and micro fibers with PVDF perform even better.

Test 9 compared the effect of adding CCA's to a small fraction of shapedPP fibers in a blend of mostly round PP fibers and shaped acrylic fibersto an identical blend that had no CCA's, only round PP fibers and shapedacrylic fibers.

Formula B included 10% PP round fibers 1.4-1.7 Dtex; 40% PP round fibers2.5 Dtex; 25% acrylic wet spun kidney bean shaped fibers 2.2 Dtex; and25% acrylic dry spun dog bone shaped fibers 3.3 Dtex.

Formula BB included 10% PP dog bone shaped fibers 1.4-1.7 Dtex with 2%PVDF; 40% PP round fibers 2.5 Dtex; 25% acrylic wet spun kidney beanshaped fibers 2.2 Dtex; and 25% acrylic dry spun dog bone shaped fibers3.3 Dtex.

Efficiency of Particle Formula Efficiency of Size (micron) A (%) FormulaBB (%) .3 49.92 83.38 .5 68.38 93.72 5 84.24 98.82 10 99.10 99.9

The material was tribo-electrically charged to approximately 2,400volts. After 30 days the charge was measured at a positive 1,475 tonegative −1,811 volts, with both negative and positive chargesthroughout the material.

With charge control agent plus fiber shape and size selection, positiveefficiencies were achieved demonstrating the improved effect bycharging, shape and size of the fiber. Considerable improvement toefficiency is seen between 0.3 and 10 microns.

Test 9 shows that adding PP dog bone shaped small denier fibers withPVDF to media causes the media to perform better than micro fiberswithout PVDF. Additionally, a small amount of dog-bone shaped microfibers helps the performance more than round micro fibers.

Test 10 tests whether a CCA on a small amount of shaped PP fibersblended with round PP fibers and shaped acrylic fibers improvesperformance over a similar blend without CCA's and only round PP fibers.

Formula C included 5% PP round fibers 1.4-1.7 Dtex; 45% PP round fibers2.5 Dtex; 45% acrylic wet spun kidney bean shaped fibers 2.2 Dtex; and5% acrylic dry spun dog bone shaped fibers 1.4-1.7 Dtex.

Formula CA included 5% PP dog-bone shaped fibers 1.4-1.7 Dtex with 2%PVDF; 45% PP round fibers 2.5 Dtex; 45% acrylic wet spun kidney beanshaped fibers 2.2 Dtex; and 5% acrylic dry spun dog bone shaped fibers1.4-1.7 Dtex.

Efficiency of Particle Formula Efficiency of Size (micron) A (%) FormulaCA (%) .3 54.61 84.62 .5 69.19 94.81 5 84.46 98.87 10 99.12 99.9

The material was tribo-electrically charged to approximately 2,800volts. After 30 days the charge was measured at a positive 1,695 tonegative −2,160 volts with both negative and positive charge throughoutthe material.

With charge control agent plus fiber shape and size selection, positiveefficiencies were achieved, thereby demonstrating the improved effect bycharging, shape and size of the fiber. Considerable improvement toefficiency is seen between 0.3 and 10 microns.

Test 10 shows that using both dry spun dog bone shaped fibers and PP dogbone shaped micro fibers show filter performance, and when PVDF is addedto the dog-bone shaped PP fibers it show another significant performanceimprovement.

Test 11 compares the effect when a blend of shaped and round PP fiberswith shaped acrylic fibers have CCA's added to the shaped PP fibers andthe shaped acrylic fibers as compared to a blend of round PP fibers andshaped acrylic fibers, neither of which have CCA's added.

Formula D included 5% PP round fibers 1.4-1.7 Dtex; 45% PP round fibers2.5 Dtex; 45% acrylic wet spun kidney bean shaped fibers 2.2 Dtex; and5% acrylic dry spun dog bone shaped fibers 1.4-1.7 Dtex.

Formula DA (one of the preferred blends) included 22.5% PP dog boneshaped fibers 2.8 Dtex with 2% PVDF; 22.5% PP round fibers 2.8 Dtex with2% non-organic wax; 5% PP dog bone shaped fibers 1.4-1.7 Dtex; 5%acrylic dry spun dog bone shaped fibers 1.4-1.7 Dtex; 22.5% acrylic wetspun dog bone shaped fibers 3.3 Dtex with 2% organic wax; and 22.5%acrylic dry spun dog bone shaped fibers 3.3 Dtex with 3-dimensionalcrimped fibers.

Efficiency of Particle Formula Efficiency of Size (micron) A (%) FormulaDA (%) .3 54.61 87.83 .5 69.19 95.66 5 84.46 98.92 10 99.12 99.93

The material was tribo-electrically charged to approximately 2,600volts. After 30 days the charge was measured at a positive 1,575 tonegative −1,825 volts with both negative and positive charges throughoutthe material.

With charge control agent plus fiber shape and size selection, positiveefficiencies were achieved, thereby demonstrating the improved effect bycharging, shape and size the fiber. Considerable improvement toefficiency is seen between 0.3 and 10 microns.

Test 11 includes a preferred blend and shows combining the best of theprior 10 tests and having PP dog-bone shaped fibers with a CCA, withsome PP 2.5 standard round fibers plus dry-spun acrylic dog bone shapedfibers with the wet spun dog bone shaped fibers with a CCA on theoutside of the fiber plus 5% each of the dog-bone shaped PP fibers andacrylic of micro fibers on the PP with a CCA added to results in thebest performing filtration media contemplated by the invention.

From the testing provided above, it is clear that the combination ofshapes and the use of charge control agents make a superiorelectrostatic performing filtration media and demonstrates the inventionis novel.

This detailed description in connection with the drawings is intendedprincipally as a description of the presently preferred embodiments ofthe invention, and is not intended to represent the only form in whichthe present invention may be constructed or utilized. The descriptionsets forth the designs, functions, means, and methods of implementingthe invention in connection with the illustrated embodiments. It is tobe understood, however, that the same or equivalent functions andfeatures may be accomplished by different embodiments that are alsointended to be encompassed within the spirit and scope of the inventionand that various modifications may be adopted without departing from theinvention or scope of the following claims.

1. A non-woven electret gas filter media comprising wet spun acrylicfibers with a dog bone cross section.
 2. The filter media in accordancewith claim 1, wherein the media includes at least some polypropylenefibers.
 3. The filter media in accordance with claim 2, wherein at leastsome of the polypropylene fibers are dog bone shaped.
 4. The filtermedia in accordance with claim 1, wherein a charge control agent isdisposed on the outer surfaces of at least some of the fibers.
 5. Thefilter media in accordance with claim 2, wherein a charge control agentis disposed on the outer surfaces of at least some of the fibers.
 6. Thefilter media in accordance with claim 3, wherein a charge control agentis disposed on the outer surfaces of at least some of the fibers.
 7. Anon-woven electret gas filter media comprising a plurality ofpolypropylene fibers with a non-round cross section.
 8. The filter mediain accordance with claim 7, wherein the media includes at least someacrylic fibers formed by a wet spinning process and having a dog bonecross section.
 9. The filter media in accordance with claim 8, whereinthe polypropylene fibers have a dog bone cross section.
 10. The filtermedia in accordance with claim 9, wherein a ratio of polypropylenefibers to acrylic fibers is in a range from about 90:10 to about 10:90.11. The filter media in accordance with claim 9, wherein thepolypropylene fibers have a round cross section.
 12. The filter media inaccordance with claim 7, further comprising a charge control agentdisposed on the outer surfaces of at least some of the fibers.
 13. Thefilter media in accordance with claim 9, further comprising a chargecontrol agent disposed on the outer surfaces of at least some of thefibers.
 14. The filter media in accordance with claim 10, furthercomprising a charge control agent disposed on the outer surfaces of atleast some of the fibers.
 15. The filter media in accordance with claim12, wherein the charge control agent is selected from the groupconsisting of organic wax, non-organic wax and PVDF.
 16. The filtermedia in accordance with claim 13, wherein the charge control agent isselected from the group consisting of organic wax, non-organic wax andPVDF.
 17. The filter media in accordance with claim 14, wherein thecharge control agent is selected from the group consisting of organicwax, non-organic wax and PVDF.
 18. A non-woven electret gas filter mediacomprising a plurality of polypropylene fibers with a charge controlagent disposed on the outer surfaces of at least some of the fibers. 19.The filter media in accordance with claim 18, wherein the media includesat least some acrylic fibers formed by a wet spinning process and havinga dog bone cross section.
 20. The filter media in accordance with claim19, wherein the polypropylene fibers have a dog bone cross section. 21.The filter media in accordance with claim 20, wherein a ratio ofpolypropylene fibers to acrylic fibers is in a range from about 90:10 toabout 10:90.
 22. The filter media in accordance with claim 20, whereinthe polypropylene fibers have a round cross section.
 23. The filtermedia in accordance with claim 18, wherein the PVDF comprises about 2percent of the weight of the media.
 24. A method of making fibers usedin a non-woven electret gas filter media, the method comprising: (a) wetspinning a plurality of acrylic fibers; and (b) during the wet spinning,adding an organic wax to water of the wet spinning process in a range ofabout 0.05 percent to about 5.0 percent, thereby leaving about 0.5% toabout 2.0% wax on the outer surfaces of at least some of the fibers. 25.The method in accordance with claim 24, further comprising the step ofblending at least some polypropylene fibers with the acrylic fibers. 26.The method in accordance with claim 24, further comprising the step ofblending at least some dog bone shaped polypropylene fibers with theacrylic fibers.
 27. A method of making a non-woven electret gas filtermedia, the method comprising: (a) dry spinning a plurality of acrylicfibers; (b) three dimensionally crimping the fibers; and (c) forming anon-woven electret gas filter media from the fibers.
 28. The method inaccordance with claim 27, further comprising the step of blending atleast some polypropylene fibers with the acrylic fibers.
 29. The methodin accordance with claim 27, further comprising the step of blending atleast some dog bone shaped polypropylene fibers with the acrylic fibers.